DESCRIPTION: The long term objective of this proposal is to define mechanisms through which metastasizing tumor cells arrest in the vasculature and extravasate from the blood stream. The proposed studies focus on the association of human melanoma cells with platelets and its role in melanoma cell adhesion to the vessel wall under flow conditions. This is relevant because evidence suggests that platelets participate in tumor extravasation. This step is rate limiting during hematogenous metastasis. The novelty of the proposed approach is the specific analysis of flow and shear stress effects on melanoma cell attachment to components of the vessel wall. Emphasis will be put on the initial contact formation and the resistance of adhesive interactions to shear forces in the presence of whole blood. This will be achieved by using a unique experimental model which mimics flow conditions in the vasculature. The flow system is combined with cofocal and video microscopy to analyze the three dimensional topography of adherent melanoma cell-platelets aggregates and to dissect and document the temporal sequence of events in dynamic adhesion processes. The goal of the proposed studies is to test the hypotheses that 1) melanoma cell interaction with platelets promotes their arrest onto the vessel wall under flow; 2) binding of melanoma cell integrin alphavbeta3 to platelet integrin alphaIIbbeta3, via divalent or multivalent RGD-containing plasma proteins as molecular bridges, provides a mechanism for specific melanoma cell-platelet interaction; and 3) the ability of melanoma cells to associate with platelets under flow in vitro relates to their metastatic potential in vivo. The role of integrins alphavbeta3 and alphaIIbbeta3 will be analyzed by using an experimentally designed human melanoma-cell model which includes cells that express either alphavbeta3 (M21-L, M21-L4, C8161) or transfected alphaIIbbeta3 (M21-LIIb), or which lack expression of both receptors (M21-L,RD). Blocking antibodies generated against these receptors will be used to confirm evidences on their function in melanoma cell-platelet interactions. Metastatic potential will be analyzed in athymic nude mice upon intravenous injection. It is anticipated that the results from these proposed studies will help to identify specific target for the therapy of malignant metastatic melanoma.